The movement, or migration, of cells (also known as cell motility) is an important part of many biological processes. Cell migration is observed in immune cells such the white blood cells which migrate to sites of infection in order to destroy bacteria or virus infected cells. Migrating cells are also observed during embryo development and in the formation of new blood vessels (a process known as angiogenesis).
Cell migration is also an important part of placental development in which cells of the placenta (the trophoblast cells) migrate into the uterus, anchoring the developing embryo and connecting to the mother's blood supply. Finally, cell migration is also observed in the spread of many cancers, in which the tumour cells migrate into the surrounding tissue and can spread to different sites in the body, a process known as metastasis.
Cell movement is a complex and tightly controlled process (shown on the right) involving the co-ordinated activity of hundreds of different proteins. In the initial stages the front end of the cell, often termed the leading edge, is pushed forward by the extension of the internal cytoskeleton. This leads to the formation of a large, flat structure that is often termed the lamellipodium. The leading edge of the cell is then attached to the surface by proteins called adhesion molecules. This allows the cell to generate traction and to pull the rest of the cell body forwards. Finally the cell detaches the back of the cell - often termed the trailing edge - and pulls it back into the main cell body. This process is then repeated as the cell continues to move forward.
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